All forms of life require that energy be conserved and stored in stable chemical compounds. The most common method of energy conservation in living organisms is the coupling of phosphorylation to electron transport. The elucidation of the mechanism of this process is one of the keys to understanding life on this planet. This proposal presents a direct attack on the mechanism of electron transport using c-type cytochromes as the experimental subjects. The main emphasis of this work has been on the kinetic mechanism of electron transport. Our work to date has been successful to a large degree and has led to the description of tentative models. Studies are now focused on determining the chemical and physical interactions controlling the functional properties of c-type cytochromes. Kinetic studies are continuing but other physical and chemical procedures are being applied to test conclusions derived. The data obtained in this work will provide two types of information: a) Information on the relation of structure and function in cytochromes. b) Information concerning the exact mechanism of electron transfer as catalyzed by c-type cytochromes. Combining all data obtained, a general picture of the mechanism of electron transport will be derived. Studies with highly purified cytochrome c will be followed by work with phospholipid-cytochrome complexes and finally with intact electron transport chains. This progression of studies will yield information on the specific modification of electron transport induced by membrane binding and coupling to energy conservation.